Abrasion resistant electric contact



ateted Jan. l6, i940 a, stares amen ATENT rrlcs ABRASION RESISTANT ELECTRIC CONTACT Franz R. Hensel, Indianapolis, Ind, assignor to P. R. Mallory & Co., Inc, Indianapolis, Ind, a corporation of Delaware No Drawing.

Serial No. 165,768

2 Claims.

' teristics.

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A more specific object of the invention is the provision of an electrical make-and-break contact formed from palladium alloys, which have been made wear resistant by a special heat treatment.

Other objects of the invention will be apparent from the following description taken in connection with the appended claims.

The present invention comprises the combination of elements, methods of manufacture, and the product thereof brought out and exemplified in the disclosure hereinafter set forth, the scope of the invention being indicated in the appended claims.

While a preferred embodiment of the invention is described herein, it is contemplated that considerable variation may be made in the method of procedure and the combination of elements without departing from the spirit of the invention.

For many purposes, such as magneto contacts, relay contacts, and the like it'has heretofore been customary to use electric make-and-break contacts composed of platinum-ruthenium or iridium-platinum alloys. While such contacts are fairly satisfactory, due to their hardness, noncorrosiveness in normal and most industrial atnoospheres, and low transfer under the electrical arcing inherent to magneto and most relay operations, they also possess the disadvantages of high initial cost and difliculty of fabrication and have usually required a fairly high percentage of iridium or ruthenium to reach the desired degree of hardness.

as a substitute for such alloys, it has been proposed to use certain palladium-silver-nickel alloys or palladium-copper-silver alloys. The disadvantage, however, with the alloys proposed, up to the present time, was thatthe alloys were either too soft or that they were very diflicult to work if the composition were chosen in such a manner as to get a high hardness in the cast or annealed condition. The present invention overcomes this disadvantage and provides an abrasion resistant palladium alloy contact material. The invention consists in using a palladium alloy containing an age-hardening ingredient forming a precipitated phase therein. Such ingredients may, for example, be elements of the silver, copper, gold group. While a straight palladiumsilver alloy forms a complete solid solution, it has been found that by the addition of copper,

Application September 25, 1937,

for instance, a material can be produced which will lend itself to improvements effected by a special heat treatment. For instance, an alloy of the composition:

Percent Pa1ladium 42 Silver 40 Copper 18 will be quite ductile and soft in the annealed condition, having a Brinell hardness of 130.

By subjecting this material to a heat treatment, consisting in quenching from above a temperature of 600 degrees (3., followed by aging below a temperature of 600 degrees 0., a hardness of over 300 Brinell can be produced and therewith an abrasion resistance heretofore unknown. The alloys are usually soft after they have been quenched from a high temperature and processing of the material can be done in the as-quenched condition, because in such condition materials are easily machinable and can be headed on a heading machine without the causing of cracks.

It has been one of the most serious disadvantages of hard alloys, consisting predominantly or at least substantially of palladium, that it is impossible to produce contact rivets from these alloys-on a heading machine. Due to the brittleness of the material, cracks are formed and the material is unsuitable for electrical contacting purposes. there are sub-microscopic or microscopic cracks in a contact material, such places will tend to cause transfer from one contact to the other. Such transfer seriously affects the satisfactory performance and in many cases might stop operation completely, because the transfer on one side becomes so large that the other contact will be interlocked with its mating contact. The general use of this type of materials, therefore, for large production of contacts made on a heading machine, has been limited, and the present invention constitutes the first attempt to produce very hard silver-palladium type alloys by conventional methods.

After the materials have been formed into the shape desired for the particular purpose, they can be subjected to a heat treatment, which will produce a hardness and an abrasion resistance heretofore unknown in electrical contact work.

Inaddition, I have found that contact materials of the silver-palladium type which are susceptible of improvement by a. double heat treatment will have a superior electrical conductivity after heat treatment, because the electrical conductivity is a function of the amount of material held in solid solution. The precipitation treatment which is applied to the contacts in the above described It is well known that whether,

manner causes the solid solution formed during quenching to disintegrate and precipitate a second phase.

It has been found possible to regulate the precipitation in such a manner that the precipitated particles are not visible under the microscope but are very finely and sub-microscopically distributed. Such a very fine structure, which is practically homogenous, has been proved to be ideally suited for electrical contact purposes. If another phase is located, for instance, in the grain boundaries, in the form of large particles, such locations will be attacked during the contact performance and the phenomenon known as material transfer will start from these heterogeneous areas. By producing the heterogeneous phases, however in such a finely distributed manner, with the above described heat treatment, I have found that the above mentioned difficulties are entirely overcome and that materials of this nature act as a quasihomogeneous.

The alloys which will show the above mentioned characteristics, may also contain such elements as, for instance, gold, tin, cobalt, or intermetallic compounds of aluminum and silicon, with cobalt, nickel, chromium, iron, molybdenum, tungsten and tantalum. As an example, I may cite that an alloy of the following composition can be hardened from the Brinell hardness of The palladium alloys are usually grouped into alloys of high palladium content, medium palladium content and lower palladium content. The high palladium content alloys contain above palladium, the medium palladium alloys contain 25-50%, and the low palladimn alloys, 10-25%.

All three types of alloys are susceptible to improvement by heat treatments, specified above. As an example of the low palladium alloy type, I might cite the following compositions:

This material in the annealed condition is quite soft. It can be hardened, however, to cover 200 Brinell by heat treatment consisting in quenching and aging. Since it is possible to vary the elements which are added to palladium base alloys, to produce by means of age hardening, abrasion resistant contacts, I do not wish to limit myself to the specific percentages set forth in this disclosure, but use them as illustrative of proportions only and not as limiting proportions.

What is claimed is:

1. An abrasion resistant electrical contacting member, consisting of substantial percentages of palladium and silver, in which gold and cobalt are present in dispersed phase.

2. An abrasion resistant electrical contacting member, consisting of substantial percentages of palladium and silver, in which intermetallic compounds of aluminium and silicon, with nickel, cobalt, chromium, iron, molybdenum, tungsten and tantalum are present in a dispersed phase.

FRANZ R. HENSEL. 

